The present invention relates generally to the field of film winding. More particularly the invention relates to taking a flat film and winding it upon a hollow core so that the film wound on the core is essentially flat. The method and apparatus of this invention is directed towards steps and mechanism to achieve a high degree of flatness of the film rolled on the core by allowing the core to be in especially close proximity to a bed roll from which it receives the film.
Multiple web winders for films, which winders wind more than one web in the same web path, have traditionally had to compromise film flatness because of the physical limitations of the winder apparatus. Ideally the film being wound is placed up against a bed roll and is kept in close tolerance to the bed roll to have an essentially wrinkle free film. In order to accomplish this result most effectively, the bed roll would have to run against the film surface being wound upon the core. However, it is difficult to control the forces between the bed roll and the core in such a way as to minimize compression of the wound film. None of the prior art technology teaches how to sufficiently balance the forces of the core to the bed roll, nor to adjust for the fact that a core changes diameter as it is being wound with the film. Also a factor in multiple web winders is that there is customarily a plurality of mandrels in the winder system and the rolls of more than one mandrel may be touching the bed roll at any given moment, each exerting a different pressure with respect to the bed roll. Because of these factors, prior art winders of multiple webs have allowed the cores to be spaced a distance from the bed roll. This is to compensate for the constantly varying core diameter as it is having film wound upon it and to allow automatic core feeding and removal. The result has been that films which are wound upon such a core customarily have a surface which is wrinkled to the degree that it is highly noticed by the consumer, a wound roll diameter which is unnecessarily large, and other undesirable attributes.
An answer to obtaining a high degree of film flatness with the use of a plastic film winder has been found in sufficiently and automatically counterbalancing the relative forces between the bed roll and the core as the core is being wound and its diameter constantly changing so that close contact between bed roll and the core upon which the film is being wound is maintained even when more than one core is in proximity to the bed roll. The present invention provides such a solution.